<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        const str = 'abc'
        console.log(str.startsWith('a')) //true
        console.log(str.endsWith('c')) //true
        console.log(str.startsWith('c',2)) //true
        console.log(str.endsWith('b',2)) //true
        console.log(str.startsWith('',100)) //false
        console.log(str.endsWith('c',100)) //true
    </script>
</body>
</html>